In a gas turbine engine hot combustion gases flow from a combustion chamber through one or more turbines which extract energy from these gases and provide power for one or more compressors and output power. Turbine blades and vanes are required to operate in extremely high temperatures and require efficient cooling if they are to withstand such temperatures.
Such cooling typically takes the form of passages formed within the blades or vanes which are supplied in operation with pressurised cooling air derived from a compressor of the gas turbine engine. This cooling air is directed through the passages in the blades or vane to provide convective or impingement cooling of the blade or vanes before being exhausted into the hot gas flow in which the blade or vane is operationally situated.
The cooling air may also be directed through small holes provided in the aerofoil surface of the blade or vane in order to provide so-called “film cooling” of the aerofoil surface.
It is known to provide hollow vanes or blades with an inner aerofoil shaped “tube” through which cooling air is passed. The inner tube is formed with holes to direct its cooling air outwardly on to the internal surfaces of the vane or blade. However, the provision of such an inner tube adds weight to the blade or vane.